On the Method of Determination of Strain Energy Release Rate During Fatigue Delamination in Composite Materials

In this paper, the problem of calculation of the energy release rate for a fatigue test on composite material has been investigated. The application of the Linear Elastic Failure Mechanics (LEFM) leads to the use of varation of the energy release rate ( G). As the energy release rate is a function of the load squared, the variation of G becomes either a function of variation of the load squared ( G = f((P²))) or a function of the square of the load variation ( G = f(( P)²)).In this paper, we determine, by different fatigue tests, which of the two theoretical results is the best to describe the experiments. These fatigue tests have been made on DCB test-specimen in mode I with different R ratios (R = P_max / P_min) and different maximum loads. The material was a unidirectionnal glass-epoxy.The results show that considering G as a function of ( P)² seems more appropriated to describe a cracking test in fatigue.